Substations for power distribution in high and medium voltage power networks include primary or field devices such as electrical cables, lines, bus bars, switches, breakers, power transformers and instrument transformers arranged in switch yards and/or bays. These primary devices are operated in an automated way via a Substation Automation (SA) system responsible for controlling, protecting and monitoring of substations. The SA system comprises programmable secondary devices, so-called Intelligent Electronic Devices (IED), interconnected in a SA communication network, and interacting with the primary devices via a process interface.
SA systems require interoperability between all IEDs independent of the manufacturer. Therefore, the IEC standard 61850 “communication networks and systems in substations” has been introduced. An abstract data model according to the standard incorporates SA functionality in terms of logical nodes grouped into logical devices and allocated to the IEDs as the physical devices. The communication-specific issues are handled via an ISO/OSI communication stack comprising a stack with MMS/TCP/IP/Ethernet and an optical, wireless or other media-type physical layer. While the data model including attributes like time stamps or validity indications is realized by the application layer of the communication stack, messages for time-critical or safety-related communication, i.e. the Generic Object Oriented Substation Events (GOOSE) such as trips and blockings, as well as for analogue Sampled Values (SV), are mapped directly to the Ethernet link layer of the communication stack.
A complete SA system with its entire devices and communication links may be described in a formal way in the engineering process by means of the comprehensive XML-based Substation Configuration description Language (SCL) for IEC 61850 compliant systems. The SCL language is used to describe the capabilities of a particular IED type in an IED Capability Description (ICD). It enumerates the communication and application functionality of the physical device as delimited e.g. by the number of I/O ports. A Substation Configuration Description (SCD) file in SCL language is a standardized configuration representation of the SA system and describes a model of a particular substation, the IED functions in terms of logical nodes, and the communication connections.
An SCD file includes the logical data flow between the IEDs in the form of control blocks specifying, for each message type or corresponding message source/service class, the receiver or intended destination IEDs, the message size in terms of data set definitions, as well as the message sending rates for all periodic traffic like GOOSE, SV and Integrity reports. Based on this information and by adding for event based reports a normal state data change rate, e.g. one changed value per second and control block, as well as a burst change size, e.g. five messages per event related control block, an average normal load as well as load peaks can be calculated for each receiver IED.
The above is used to advantage in the patent application EP-A 2157731. From a logical data flow description that is part of a standardized configuration representation of a SA system and which includes, in the form of control blocks, formal information for every message, receiver IEDs are retrieved or determined. For each retrieved receiver IED, the totality of all network messages destined for or directed to this particular receiver IED is evaluated or processed, e.g. in view of a subsequent network load analysis, Virtual Local Area Network assignment, or graphical display of the data flow. The process is applied to engineered SA systems and thus unable to detect hardware failures that may result in broadcasting of excessive message rates or configuration errors that are only introduced during installation or commissioning when configuration information previously engineered is transferred to the IEDs. Hardware failure and configuration inconsistencies between the SCD file and the actual configuration of an individual IED should be identified and remedied during or after a commissioning of an SA system.
A mere size aspect adds to the aforementioned configuration inconsistency issues. For large process control systems with increased real time critical communication needs due to multicast communication traversing the entire system, the communication network load becomes critical. Furthermore, engineers from different parties independently configuring data servers may not be aware of the communication needs and restrictions of the respective clients, and generally have no focus on the complete system communication load. This is especially true for multicast GOOSE and SV messages according to IEC 61850, and has an impact on the entire communication system as well as on individual message receivers. Hence completeness and/or correctness of the data flow definitions, particularly in process control systems with up to 500 IEDs communicating among each other, are not easily verified. In this context, the principles and methods of the following invention are by no means restricted to a use in substation automation, but likewise applicable to other process control systems with a standardized configuration description. In particular, it has to be noted that IEC 61850 is also an accepted standard for Hydro power plants, Wind power systems, and Distributed Energy Resources (DER).
As mentioned, IEC 61850 based process control systems offer, in addition to the standardized communication based on Ethernet and for some service types on TCP/IP, a standardized description of the data models and communication definitions inside all server IEDs based on SCL. Furthermore the standardized description also allows relating all IP addresses to client IEDs, even if the latter do not support directory services for data model and logical device name discovery. On the other hand, within such kinds of communication systems clients risk to be overloaded to an extent preventing them from processing any further incoming data.
The reasons for this may be manifold and include hardware faults in the system generating excessive messages, as well as, most prominently, inconsistent or wrong configuration of the servers concerning the client functionality. Although the effects caused by the communication overload at the receiver can be immediately observed, it is not easy to diagnose the cause. If communication problems arise, special communication diagnostic facilities implemented in each client may be enabled. The latter however are client specific and rely on specific knowledge of the client IED type.
Alternatively a protocol analyser may be used to collect and analyse communication traffic. With the growing dependency on Ethernet communication between IEDs and other devices in a substation, tools have been developed that allow for analysis of the network traffic, i.e. basic Ethernet and related TCP/IP traffic, being exchanged in a SA network. A few of these (mms-ethereal, KEMA Analyzer) allow to further analyse standard Ethernet traffic and extract 61850 relevant data packets such as Sampled values, GOOSE, MMS etc. from the messages. However, there is no possibility for an operator to understand the context of this extracted data, i.e. to give it a correct meaning.
The patent application EP-A 1 850 447 describes a Substation Automation testing tool which combines protocol semantics information found in the SCL (Substation Configuration Language) File of a substation (Substation Configuration Description) or an IED (IED Capability description) with substation-relevant data extracted from the Substation Communication network traffic. By means of a standard laptop computer as a message interceptor connected to a substation communication network, IEC 61850 relevant data is retrieved and analysed, allowing for consistency verification without revision handling.
The patent application EP-A 2 288 080 is concerned with an analysis of a communication stack performance of an IED in a communication network of a SA system. A plurality of application level scenario corresponding to a high communication load on the IED is executed by means of a message synthesizer. Among all network messages intercepted during scenario execution, those network messages destined to the IED and sent by the IED in response are identified. An IED-intrinsic processing time of the identified messages is likewise determined, based on which parameter values of an IED processing time model for a specific communication service are calculated.